Gapping of MnO, FeO, CoO, and NiO Mott insulators by SCAN without U*

Mott insulation is generally enabled by the physics of symmetry conserving on-site interelectronic repulsion U on single 3d sites via the celebrated Hubbard Model. DFT, exact for the ground state properties in principle, can not consistently open band gaps for MnO, FeO, CoO, and NiO Mott insulators if one uses symmetry conserving structures along with conventional semi local approximations to its exchange correlation functional. It has been recently shown [1] that using energy-lowering symmetry breaking mechanisms, DFT+U which distinguishes occupied and empty orbitals, opens band gaps for the monoxides. Here we show that even without invoking U, the semi local SCAN density functional [2] whose potentials are orbital dependent via the kinetic energy density dependence, opens band gaps for the monoxides in their AFM and PM (modeled with SQS) phases. The mechanism of gapping is analyzed. This success revives DFT for d electron materials and encourages the development of more sophisticated density functionals.
[1] G. Trimarchi, et al, PRB, 97, 035107 (2018).
[2] J. Sun, et al, RRL 115, 036402 (2015).